allow user to opt out from the mailing list
The mailing lists allgo-announce-dev and allgo-announce-user are generated automatically from the users table.
- users have no way to opt out
- users cannot delete their account (feature not implemented)
- the ml should have a footer to all outgoing email « You are receiving this e-mail because you have a user account at https://allgo.inria.fr. You can opt out from the mailing list or delete your account at https://allgo.inria.fr/users/edit. »
Edited by BAIRE Anthony